diff --git a/codersdk/toolsdk/chats.go b/codersdk/toolsdk/chats.go
index 8647e4bed44..0f94b185124 100644
--- a/codersdk/toolsdk/chats.go
+++ b/codersdk/toolsdk/chats.go
@@ -97,7 +97,7 @@ The chat runs asynchronously. Poll coder_get_chat for status and read the transc
 				},
 				"organization_id": map[string]any{
 					"type":        "string",
-					"description": "Optional organization UUID. Defaults to the authenticated user's first organization.",
+					"description": "Optional organization UUID. Defaults to the organization of the authenticated user's most recently updated chat. If the user has never created a chat, defaults only when they belong to one organization.",
 				},
 				"model_config_id": map[string]any{
 					"type":        "string",
@@ -125,15 +125,11 @@ The chat runs asynchronously. Poll coder_get_chat for status and read the transc
 				return ChatToolStatus{}, xerrors.New("organization_id must be a valid UUID")
 			}
 		} else {
-			me, err := deps.coderClient.User(ctx, codersdk.Me)
+			var err error
+			orgID, err = defaultCreateChatOrganization(ctx, deps)
 			if err != nil {
 				return ChatToolStatus{}, err
 			}
-			// Admins can remove a user's only organization membership.
-			if len(me.OrganizationIDs) == 0 {
-				return ChatToolStatus{}, xerrors.New("authenticated user belongs to no organization; pass organization_id explicitly")
-			}
-			orgID = me.OrganizationIDs[0]
 		}
 		var modelConfigID *uuid.UUID
 		if args.ModelConfigID != "" {
@@ -159,6 +155,44 @@ The chat runs asynchronously. Poll coder_get_chat for status and read the transc
 	},
 }
 
+func defaultCreateChatOrganization(ctx context.Context, deps Deps) (uuid.UUID, error) {
+	me, err := deps.coderClient.User(ctx, codersdk.Me)
+	if err != nil {
+		return uuid.Nil, err
+	}
+	// Admins can remove a user's only organization membership.
+	if len(me.OrganizationIDs) == 0 {
+		return uuid.Nil, xerrors.New("authenticated user belongs to no organization; pass organization_id explicitly")
+	}
+	if len(me.OrganizationIDs) == 1 {
+		return me.OrganizationIDs[0], nil
+	}
+
+	expClient := codersdk.NewExperimentalClient(deps.coderClient)
+	chats, err := expClient.ListChats(ctx, &codersdk.ListChatsOptions{
+		Source: codersdk.ChatListSourceCreatedByMe,
+		Pagination: codersdk.Pagination{
+			Limit: 100,
+		},
+	})
+	if err != nil {
+		return uuid.Nil, xerrors.Errorf("list chats to determine organization: %w", err)
+	}
+	// Pinned chats sort before recently updated chats. If the user has 100
+	// pinned chats, this batch may not contain their latest chat, which is an
+	// acceptable tradeoff for keeping organization selection to one request.
+	var latest *codersdk.Chat
+	for i := range chats {
+		if latest == nil || chats[i].UpdatedAt.After(latest.UpdatedAt) {
+			latest = &chats[i]
+		}
+	}
+	if latest != nil {
+		return latest.OrganizationID, nil
+	}
+	return uuid.Nil, xerrors.New("organization_id is required because the authenticated user belongs to multiple organizations and has not created a chat yet")
+}
+
 type GetChatArgs struct {
 	ChatID string `json:"chat_id"`
 }
diff --git a/codersdk/toolsdk/chats_test.go b/codersdk/toolsdk/chats_test.go
index c6a36158af8..e50ab4db7c1 100644
--- a/codersdk/toolsdk/chats_test.go
+++ b/codersdk/toolsdk/chats_test.go
@@ -122,8 +122,9 @@ func TestChatTools(t *testing.T) {
 		ctx := testutil.Context(t, testutil.WaitLong)
 
 		created, err := testTool(t, toolsdk.CreateChat, tb, toolsdk.CreateChatArgs{
-			Prompt: "Say hello.",
-			Labels: map[string]string{"purpose": "toolsdk-test"},
+			Prompt:         "Say hello.",
+			OrganizationID: firstUser.OrganizationID.String(),
+			Labels:         map[string]string{"purpose": "toolsdk-test"},
 		})
 		require.NoError(t, err)
 		chatID, err := uuid.Parse(created.ID)
@@ -736,8 +737,9 @@ func TestChatTools(t *testing.T) {
 		blockingModelConfig := coderdtest.CreateOpenAICompatChatModel(t, expClient, blockingURL)
 
 		created, err := testTool(t, toolsdk.CreateChat, tb, toolsdk.CreateChatArgs{
-			Prompt:        "Block forever.",
-			ModelConfigID: blockingModelConfig.ID.String(),
+			Prompt:         "Block forever.",
+			OrganizationID: firstUser.OrganizationID.String(),
+			ModelConfigID:  blockingModelConfig.ID.String(),
 		})
 		require.NoError(t, err)
 		require.Equal(t, codersdk.ChatStatusRunning, created.Status)
@@ -794,6 +796,59 @@ func TestChatTools(t *testing.T) {
 		require.Contains(t, auditorIDs, defaultModelConfig.ID.String())
 	})
 
+	t.Run("CreateChatUsesLastUpdatedOrganization", func(t *testing.T) {
+		ctx := testutil.Context(t, testutil.WaitLong)
+		model := coderdtest.CreateOpenAICompatChatModel(t, expClient, "")
+		organization := dbgen.Organization(t, api.Database, database.Organization{})
+		dbgen.OrganizationMember(t, api.Database, database.OrganizationMember{
+			OrganizationID: organization.ID,
+			UserID:         firstUser.UserID,
+		})
+		defaultOrgChat := dbgen.Chat(t, api.Database, database.Chat{
+			OrganizationID:    firstUser.OrganizationID,
+			OwnerID:           firstUser.UserID,
+			LastModelConfigID: model.ID,
+		})
+		dbgen.Chat(t, api.Database, database.Chat{
+			OrganizationID:    organization.ID,
+			OwnerID:           firstUser.UserID,
+			LastModelConfigID: model.ID,
+		})
+
+		err := expClient.UpdateChat(ctx, defaultOrgChat.ID, codersdk.UpdateChatRequest{
+			Archived: ptr.Ref(true),
+		})
+		require.NoError(t, err)
+		err = expClient.UpdateChat(ctx, defaultOrgChat.ID, codersdk.UpdateChatRequest{
+			Archived: ptr.Ref(false),
+		})
+		require.NoError(t, err)
+
+		created, err := testTool(t, toolsdk.CreateChat, tb, toolsdk.CreateChatArgs{
+			Prompt:        "Reuse the last updated organization.",
+			ModelConfigID: model.ID.String(),
+		})
+		require.NoError(t, err)
+		chat, err := expClient.GetChat(ctx, uuid.MustParse(created.ID))
+		require.NoError(t, err)
+		require.Equal(t, firstUser.OrganizationID, chat.OrganizationID)
+	})
+
+	t.Run("CreateChatRequiresOrganizationForNewMultiOrgUser", func(t *testing.T) {
+		organization := dbgen.Organization(t, api.Database, database.Organization{})
+		memberClient, member := coderdtest.CreateAnotherUser(t, client, firstUser.OrganizationID)
+		dbgen.OrganizationMember(t, api.Database, database.OrganizationMember{
+			OrganizationID: organization.ID,
+			UserID:         member.ID,
+		})
+		memberDeps, err := toolsdk.NewDeps(memberClient)
+		require.NoError(t, err)
+
+		_, err = testTool(t, toolsdk.CreateChat, memberDeps, toolsdk.CreateChatArgs{Prompt: "hi"})
+		require.ErrorContains(t, err, "belongs to multiple organizations")
+		require.ErrorContains(t, err, "organization_id is required")
+	})
+
 	t.Run("CreateChatZeroOrgUser", func(t *testing.T) {
 		ctx := testutil.Context(t, testutil.WaitLong)